Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $197.59   13.352%   $223.9722   $223.97   $223.95   $224.00  
  Purchase #2 $26.36   13.617%   $29.9494   $29.95   $29.95   $29.90  
  Purchase #3 $74.63   10.134%   $82.193   $82.19   $82.20   $82.20  
  Purchase #4 $126.99   3.266%   $131.1375   $131.14   $131.15   $131.10  
  Purchase #5 $221.31   11.110%   $245.8975   $245.90   $245.90   $245.90  
  Purchase #6 $124.50   6.570%   $132.6797   $132.68   $132.70   $132.70  
  Purchase #7 $106.80   10.717%   $118.2458   $118.25   $118.25   $118.20  
  7 purchase totals = $878.18       $964.0751   $964.08   $964.10   $964.00